<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>cacl函数</title>
    <style>
        .father {
            width: 300px;
            height: 200px;
            background-color: aquamarine;
        }

        .son {
            /* 发出了警告，该句并没有被执行 */
            width: calc(100%-50px);
            height: 30px;
            background-color: pink;
        }
    </style>
</head>

<body>
    <!-- 要求我们子盒子宽度永远比父盒子宽度小30px -->
    <div class="father">
        <div class="son"></div>
    </div>
</body>

</html>